Normal brake/park light bulb of bikes consumes high watts,say in my bike 12volt,21watts/5 watts,which sucks the battery and after few years,battery dies and horn doesnt sound when brakes applied. so i converted my bike danger light into led bulb,
for brake light i used 1 watt luxeon red and for park light i used 3 8mm white led's.
i broke the oem bulb and used the metal part of bulb to fix the led board,
now my bike has a bright led bulb that consumes 5 watts/1 watts,and is brighter than oem,
advantages: horn sounds well,headlights are brighter.

the circuit has been designed with lm317 as a constant current source,
V/I=R
1.25/0.35=3.57ohms
use 3.9ohms,1watts resistor with lm317 with small heatsink for lm317.
the three white led's are 70ma led,
so using 56ohms,1/2 watts will drive three leds.